A question for women who have been pregnant.

I just started trying this past week to get pregnant. I looked at the calendar and I am at the right point in my cycle. We had sex 3 times this week and then again this morning. Now I am having painful cramps in my uterus that feel like my period, however I am not due for my period. Have any women here experienced cramping after conception? My friend said she did after she conceived her daughter. Should I be worried? I also feel slightly nauseated, but I think that is just from the pain. Could it be an ectopic pregnancy this early on?